DOPING LIMITS OF C, BERYLLIUM, AND SI IN GAAS GROWN BY SOLID SOURCE MOLECULAR-BEAM EPITAXY WITH A THERMALLY CRACKED AS2 SOURCE

The maximum doping limits for C, Be, and Si in GaAs grown by solid source molecular-beam epitaxy using As2 derived from a high temperature Ta cracker have been investigated. The C and Si-dopant fluxes were obtained from resistively heated filaments, whereas Be was evaporated from pyrolytic BN crucible in an effusion cell. The maximum electrical carrier concentrations determined by Hall measurements were 6, 20, and 1.6 x 10(19) cm-3 for C, Be, and Si, respectively. The maximum carrier densities for Be and Si-doping were obtained at a relatively low growth temperature around 480-degrees-C, whereas for C-doping, the optimum growth temperature is around 600-degrees-C. This difference is attributed to the temperature dependence of the surface vacancy concentration ratio [V(Ga)]/[V(As)], which affects the incorporation of substitutional dopant atoms. Secondary ion mass spectrometry data shows substantial in-diffusion of Be concentrations above the solubility limit for a given growth temperature.